re: Tropical Storm Nicholas - Flash Flood Watch for South Louisiana

The HRRR isn't favoring any rotation/training bands and is basically treating it like a front and moving it through at a steady, but slow pace.

The NAM, though, is accounting for that rotation and still has the possibility of training bands later on this evening. Looking at current radar, I tend to favor that solution. The HRRR seems to be struggling with the decoupling, as has been the trend with it for a while now with this system.

State offices closed in EBR Wednesday. Does this have any effect historically in ebr schools also closing?

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State offices closed in EBR Wednesday. Does this have any effect historically in ebr schools also closing?

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Historically speaking, yes

I didnt get to sleep at a Holiday Inn last night, because they cancelled my reservation for some evacuees, so help me understand this . . . .

Does the path of the storm matter at all in this case, if the convection is being sheared away from of it?

Nola is projected to get 6-10” from tonight and tomorrow?

Radar shows Nola is almost in the clear

With schools you never know but if state offices are really closing, schools usually follow. I hope they can go to school. For me wife's sanity

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Nola is projected to get 6-10” from tonight and tomorrow?

Radar shows Nola is almost in the clear

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It's going to refire tonight.

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Summary...Heavy rainfall associated with Tropical Storm Nicholas
will continue to plague portions of the Central Gulf Coast through
this evening. Rain rates of 1-2"/hr are likely, which could
produce 1-3" of rain with local amounts to 5". Flash flooding is
likely.

Discussion...Tropical Storm Nicholas was located at 1800 UTC about
30 miles SE of Houston, TX moving ENE at 7mph. The center of
circulation is clearly evident on the regional radar mosaic, with
heavy rainfall almost exclusively confined east and well east of
the center. Recently, some narrow convergence bands had developed
east of Galveston Bay with heavy rain lifting again into the far
Upper Texas Coast, but otherwise most of the rainfall was east of
Vermilion Bay and across southeast Louisiana where recent rainfall
rate estimates from KLIX were as high as 2"/hr. This has led to
CREST unit streamflow measurements above 700 cfs/smi, and flash
flooding is continuing across the area.

As T.S. Nicholas continues to drift eastward through this evening,
heavy rain will persist near the Central Gulf Coast. Guidance has
trended a bit eastward with the heaviest rainfall, and this
appears to be due to some drier continental air which is advecting
around Nicholas and is clearly evident in CIRA LPW fields. East of
this drier air, the thermodynamics remain extremely favorable for
heavy rainfall with PWs of 2.1 to 2.3 inches on the special 18Z
U/A soundings from KLIX and KLCH, respectively. Additionally,
freezing levels are near 16,000 ft, suggesting efficient warm rain
processes. This is leading to widespread rainfall rates of around
1"/hr, and the HREF probabilities indicate an increasing
likelihood for 2-3"/hr this evening, focused in southeast
Louisiana.

Despite drier air approaching from the west, there is likely to be
a window of significant overlap of forcing and moisture to drive
excessive rainfall through this evening. A pronounced inflow band
continues to extend into the Gulf of Mexico on the leading edge of
this drier air, while an effective coastal/warm front lies near
the coast of Louisiana at the nose of the WAA/LLJ serves as an
additional focus for low-level convergence. As Nicholas shifts
eastward, 925-850mb flow should increase out of the S/SW to more
impressively shift moisture and instability northward, while at
the same time the S/SE flow from the central Gulf intensifies.
This could produce a situation where the most intense moisture
advection within the primary inflow band begins to isentropically
ascend the slow moving effective front, leading to an axis of
continuous 2"+/hr rainfall. The exact placement of this still
varies within the various high-res guidance, but the trend has
been to focus over far southern Louisiana, with recent runs of the
HRRR all shifting SE, to be more aligned with the CONEST and ARW2.
Where this occurs, additional rainfall in excess of 5" is
possible, with 1-3" expected elsewhere across the region. Flash
flooding is likely.

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Nope dont like that map or those hourly rates.

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As Nicholas shifts
eastward, 925-850mb flow should increase out of the S/SW to more
impressively shift moisture and instability northward, while at
the same time the S/SE flow from the central Gulf intensifies.

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This is the player that will re-fire the convection/rain off of the coast and drag it Northward throughout the night. NOLA East to around Gulport could be the bullseye for that rain. Slidell getting in that little bit of a dry slot for the past couple hours will hopefully help them. Gulport needs a break right now, though.